(NaturalNews) Men are being enslaved and forced to work for no pay at all, and for years at a time, under threat of extreme harm in Asia as part of the global production of seafood for major U.S., British and other European retailers, according to a British newspaper.

Following a six-month investigation, The Guardian reported recently that large numbers of men have been bought and sold like chattel and then held against their will on fishing boats off Thailand. Apparently, the paper said, the slaves have become "integral to the production of prawns (commonly called shrimp in the US) sold in leading supermarkets around the world, including the top four global retailers: Walmart, Carrefour, Costco and Tesco."

The newspaper's investigation found that the world's largest shrimp farmer, Thai-based Charoen Pokphand (CP) Foods, buys fishmeal, which it then feeds to its farmed shrimp, from suppliers who own, operate or buy from fishing boats that are manned, in part, by slaves.

As published in the paper:

Men who have managed to escape from boats supplying CP Foods and other companies like it told the Guardian of horrific conditions, including 20-hour shifts, regular beatings, torture and execution-style killings. Some were at sea for years; some were regularly offered methamphetamines to keep them going. Some had seen fellow slaves murdered in front of them.

Fifteen migrant workers from Burma and Cambodia also told how they had been enslaved. They said they had paid brokers to help them find work in Thailand in factories or on building sites. But they had been sold instead to boat captains, sometimes for as little as [$420].

'We'd get beaten even if we worked hard'

"I thought I was going to die," Vuthy, a former monk from Cambodia who was sold from captain to captain, told the paper. "They kept me chained up, they didn't care about me or give me any food ... They sold us like animals, but we are not animals -- we are human beings."

Another victim of the horrific human trafficking told a story about how he had witnessed as many as 20 fellow slaves murdered outright in front of him; one was tied, limb by limb, to the bows of four boats and subsequently pulled apart while at sea, he said.

"We'd get beaten even if we worked hard," another said. "All the Burmese, [even] on all the other boats, were trafficked. There were so many of us [slaves] it would be impossible to count them all."

The Guardian reports that CP Foods -- which has annual revenues of $33 billion and brands itself as "the kitchen of the world" -- sells its own name-brand shrimp feed to other farms. It also supplies international supermarkets, as well as a number of food makers and food retailers, with frozen or cooked shrimp and ready-made meals. The company also sells raw shrimp materials for food distributors.

Besides the aforementioned mega-retailers, the paper identified other British supermarket chains such as Aldi, Morrisons, the Co-operative and Iceland as additional CP Foods customers. All of them sell frozen or cooked shrimp, or various shrimp-laced ready-to-cook meals and stir fry.

What's more, CP Foods has admitted that slave labor is a part of its supply chain.

"We're not here to defend what is going on," said Bob Miller, CP Foods' UK managing director. "We know there's issues with regard to the [raw] material that comes in [to port], but to what extent that is, we just don't have visibility."

'If you by shrimp from Thailand, you will be buying the produce of slave labor'

The Guardian shed light on that:

The supply chain works in this way: Slave ships plying international waters off Thailand scoop up huge quantities of "trash fish", infant or inedible fish. The Guardian traced this fish on landing to factories where it is ground down into fishmeal for onward sale to CP Foods. The company uses this fishmeal to feed its farmed prawns, which it then ships to international customers.

Alarm over the cruel use and treatment of slaves in the Thai fishing industry has been sounded in the past, via the United Nations and non-governmental organizations. But for the first time, the paper has managed to establish how all of the pieces of the long, complicated supply chain operates in practice, and how slavery is intricately connected to it and to the retailers that the industry supplies.

"If you buy prawns or shrimp from Thailand, you will be buying the produce of slave labour," said Aidan McQuade, director of Anti-Slavery International.

Via international law and treaty, slavery is illegal in every country in the world.

Guardian report builds off earlier findings

A 2013 report by the Environmental Justice Foundation (EJF) titled "The Hidden Cost: Human Rights Abuses in Thailand's Shrimp Industry" notes that the country is the largest exporter of shrimp in the world, exporting over 392,000 tons in 2011; 46 percent of that shrimp went to the U.S., while Thailand accounted for more than 10 percent of Europe's total shrimp imports.

"The shrimp industry is heavily reliant on migrant workers, many of whom are trafficked and face arduous journeys before having to endure abusive conditions in Thailand's exploitative shrimp factories," the report said. "Due to a desire to keep costs as low as possible, major exporting companies often subcontract to external pre-processing facilities. These facilities, also referred to as 'peeling sheds', remove the heads, veins and hard shell of shrimp and prepare it for secondary or value-added processing. This pre-processing stage of production is the most labor-intensive and least regulated aspect of an otherwise sophisticated supply chain. This informal nature makes it particularly prone to poor working conditions, breaches of national and international labor standards, child and forced labor, exploitation and abuse."

The organization's own investigation found that some of the most serious issues plaguing the shrimp industry in that part of the world include "human trafficking, exploitation, bonded and child labour," which EJF says "remain widespread." One of the biggest culprits is lack of industry regulation and effective monitoring, which the group says makes it difficult to truly gauge the breadth of abuse.